One method of determining that a chain has become worn and is in need of replacement is by measuring the amount by which the chain has become elongated from its original length. This measurement is particularly important in applications in which the links of the chain are adapted to engage one or more sprockets, as in a bicycle or motorcycle, or chain-driven equipment. In such systems, the distance between adjacent links of the chain must match the distance between adjacent teeth on the sprocket in order for the force from the chain links to be evenly distributed across all of the teeth engaged by the chain links. If a chain becomes elongated, then only a few of the links will drive (or be driven by) the sprocket teeth, and the remaining links will be slightly spaced between adjacent teeth. An elongated chain will slip on the sprockets and this slippage will cause frictional and impact wear on the sprockets, thereby damaging the sprockets. For a bicycle rider, chain slippage will result in some discomfort because peddling the bicycle is less smoothly accomplished. Further, as elongation worsens, chain slippage worsens, damage to the sprockets increases, and the chain becomes unusable. It is therefore desirable to accurately measure the elongation of a chain so that a chain may be replaced before detrimental slippage on sprockets occurs.
One device that measures chain wear is disclosed in Stinnett U.S. Pat. No. 3,998,317. Stinnett discloses a chain wear indicator for conveyor chains. The Stinnett device measures the wear of individual links of a chain by inserting a tapered projection into the gap between links until the sides of the projection engage the opposite sides of the gap. The further the tapered projection is inserted before it engages the sides of the gap, the greater the distance between the links. However, the Stinnett device only measures the width of the gap between two individual links, which is not necessarily an indication of chain elongation.